1. Field of the Invention
The present invention relates generally to a turbopump, and more specifically to a rocket engine turbopump with high output pressure.
2. Description of the Related Art Including Information Disclosed Under 37 CFR 1.97 and 1.98
A turbopump is a turbine driven pump that comprises of two main components: a pump and a driving turbine, usually both mounted on the same shaft, or sometimes geared together. The purpose of a turbopump is to produce a high pressure fluid for feeding a combustion chamber or other use. A turbopump generally comprise one of two types of pumps: centrifugal pump, where the pumping is done by throwing fluid outward at high speed; or axial flow pump, where helical style blades progressively raise the pressure of a fluid.
Axial flow pumps have small diameters, but give relatively modest pressure increases. They are generally used to raise the pressure gradually in order to prevent cavitation of the centrifugal pump. Centrifugal pumps are far more powerful for high density fluids, but require physically large diameters for low density fluids. Turbopumps operate in much the same way as turbo units for vehicles. Higher fuel pressures allow fuel to be supplied to higher-pressure combustion chambers for higher performance engines.
Turbopumps have a reputation for being extremely hard to design to get optimum performance. Whereas a well-engineered and debugged pump can manage 70-90% efficiency, figures less than half that are not uncommon. Low efficiency may be acceptable in some applications, but in rocketry this is a severe problem. Turbopumps in rockets are important and problematic enough that launch vehicles using one have been caustically described as a ‘turbopump with a rocket attached’—up to 55% of the total cost has been ascribed to this area. Common problems include: excessive flow from the high pressure rim back to the low pressure inlet along the gap between the casing of the pump and the rotor; excessive recirculation of the fluid at inlet; excessive vortexing of the fluid as it leaves the casing of the pump; and, damaging cavitation to impeller blade surfaces in low (fluid) pressure zones. In addition, the precise shape of the rotor itself is critical.